FIG. 3 of the accompanying drawings shows a conventional CO.sub.2 laser oscillator device. The laser oscillator device includes an electric-discharge tube 1 having an output coupling mirror 2 and a total reflection mirror 3 that are positioned in opposite ends of the electric-discharge tube 1. Metal electrodes 4, 5 are installed on the outer circumference of the electric-discharge tube 1. When a high-frequency voltage is applied between the metal electrodes 4, 5 by a high-frequency power supply 6, a high-frequency glow discharge is produced in the electric-discharge tube 1 for laser excitation. A laser beam axis in the electric-discharge tube 1 is indicated at 13, whereas a laser beam axis extending out of the tube 1 from the output coupling mirror 2 is indicated at 14.
To start the laser oscillator device, a gas in the device is first evacuated by a vacuum pump 12. Then, a valve 11 is opened to introduce a prescribed amount of laser gas from a gas container 10 into the device until the pressure of the gas in the device reaches a predetermined pressure level. Subsequently, the device is continuously evacuated by the vacuum pump 12 and continuously replenished with the laser gas through the valve 11. The laser gas in the device is therefore continuously replaced with a fresh gas while the gas pressure in the apparatus is being kept at the predetermined pressure level. In this manner, the laser gas in the device is prevented from being contaminated.
In FIG. 3, the laser gas is circulated in the device by a roots blower 9 so that the laser gas is cooled. With the CO.sub.2 gas laser, about 20% of the applied electric energy is converted into a laser beam, and the rest is consumed to heat the laser gas. According to the theory, however, since the gain of laser oscillation is proportional to the minus (3/2)th power of the absolute temperature T, it is necessary to forcibly cool the laser gas in order to increase the oscillation efficiency. In the illustrated device, the laser gas flows through the electric-discharge tube 1 in the direction indicated by the arrows at a speed of about 100 m/sec. and is introduced into a cooling unit 8. The cooling unit 8 mainly removes the heat energy produced by the electric discharge from the laser gas. Since the gas blower 9 heats the laser gas when it compresses the laser gas, the laser gas from the gas blower 9 is passed through a cooling unit 7 before the laser gas is introduced into the electric-discharge tube 1 again. The cooling units 7, 8 will not be described in detail as they are well known in the art.
The conventional laser oscillator device illustrated in FIG. 3 has the following problems:
The first problem is that since the roots blower is a low-speed volumetric blower, it is large in size and weight, and the laser oscillator itself is large.
According to the second problem, the roots blower sends a pulsating gas flow, and the output power of the laser is affected by the pulsating gas flow.
The third problem is that the roots blower 9 produces a considerable level of vibration which adversely affects the pointing stability of the laser beam.